Abstract

The prevalence of food allergy is increasing in westernized countries, affecting 5-8% of children and 1-3% of adults. Although innumerous proteins are encountered in normal diets, only few proteins are commonly implicated as food allergens. In this vein, the major focus in allergy studies falls into intrinsic features of allergens; however, it is known that extrinsic factors can play a role in allergic processes. The allergenicity of Ber e 1, the major allergen from Brazil nuts, is well established and it has been shown that natural lipids from Brazil nuts are essential for the development of an immune response towards Ber e 1. The present study aimed to characterize the humoral response induced by recombinant (r)Ber e 1 alone or in the presence of lipids, and to investigate the mechanism(s) by which natural lipids influence the development of an immune response. BALB/c mice were sensitised intraperitoneally with rBer e 1 alone or in the presence of different lipid fractions. It was found that rBer e 1 alone did not induce an immune response and only one specific fraction of Brazil nut lipids (SPC fraction C), composed of a mixture of lipid classes, was able to induce a Th2-type humoral response, with the presence of Ber-specific anaphylactic antibodies, high levels of Ber-specific IgG1, and low levels of Ber-specific IgG2a. CD1-restricted natural killer (NK)T cells recognize lipids and therefore to test the hypothesis that NKT cells may be involved in the response, the sensitisation protocol with rBer e 1 and SPC lipid fraction C was tested in mice lacking these cells (J18 KO mice). These animals presented significantly lower titers of Ber-specific anaphylactic antibodies, Ber-specific IgG1, and total IgE than sensitised wild type mice, indicating that one of the pathways by which lipids triggered an immune response involved NKT cells. In conclusion, the present work found

that lipids from Brazil nuts were essential for the development of a Th2-type humoral response to rBer e 1 and that the immune response induced by lipids involved NKT cells.